A well-known, and very useful, separable fastener, well-known as VELCRO, includes a first fastening element having fibers or other hook-engaging means and a second fastening element having plastic or other hook defining means. In the mated condition of the two fastening elements, the several hooks releasably engage the fibers in such a way that the fastening elements are separably fastened together.
Menzin et al, in U.S. Pat. Nos. 3,752,619, 3,758,657, 3,762,000, each incorporated herein by reference, disclose and claim machine, method, and separable fastening element that relate to this kind of separable fastener. The utility is limited, however, because there are several significant disadvantages associated with the Menzin et al technology.
A forming disk, mounted for rotation with a shaft, has a groove in its peripheral wall into which plural, circumferentially-spaced modules are received, with the generally radial edges of circumferentially-adjacent modules in abutting relation. Each module includes interdigited mold and spacer plates, and because of the abutting relation between the generally radial edges of the plates of adjacent modules, and further because the spacer plates need to move radially inward and outward, the position of the mold and of the spacer plates must be in an alternating relation in circumferentially-adjacent modules. The circumferential surfaces of the mold and spacer plates of the several modules are curved. As will be appreciated, the modules thus require very-precise, and costly, machining to both insure proper interleaving and close-fit at the radial interfaces so as to provide continuous, gap-free molding surfaces and effective ribbon release out of the mold cavity. By way of example, if the constitutive mold and spacer plates are out of tolerance of one or two thousands of an inch, the machine suffers severe performance degradation.
An injection head is provided proximate a point along the circumference of the forming disk. A first nozzle is provided in the injection head for injecting plastic material into hook-like cavities of the mold plates and a second, downstream injection nozzle is provided in the injection head for applying a backing layer of plastic backing to the plastic already injected into the hook-like cavities. First and second pumps are coupled to the first and second injection nozzles for forcing the plastic material into the mold cavities and onto the surface of the modules. But because the pumps must force the plastic material into the mold cavities, and onto the forming disk, the pumps must be operated at comparatively-high pessure. High-pressure pumps tend to wear and are consumed in proportion to the pump pressure, so that at the comparatively-high pressures actually employed, the pumps are periodically subject to premature failure. At such times, not only are significant materials and labor costs involved in pump replacement, but system throughput is interrupted, production is lost, and product revenue consequently is diminished.
Further disadvantages are associated with the way that only non-uniform hook patterns are provided on the ribbon as produced. The position of the mold plates and the spacer plates of circumferentially-adjacent modules are in alternating relation, so that in one module, for example, if the laterally outer plate is a mold plate and the next laterally inward plate is a spacer plate, in the circumferentially adjacent modules, the laterally outer plate is a spacer plate and the next plate adjacent thereto is a mold plate. The spacer plates of adjacent layers overlap and interleave at the generally radial interface of circumferentially-adjacent modules. Because of this radial interface interleaving the thickness of the spacer plates and mold plates in each module, and module to module, must be the same, so that the hooks of the ribbon, as produced by each given module, are non-uniformly spaced across the width of each module. Moreover, the hooks as formed in the alternating-position mold plates between circumferentially adjacent modules, are in laterally offset staggering relation, so that thereby the hooks are non-uniformly spaced module-to-module along the length of the produced ribbon. The non-uniform hook pattern, described above, presents special difficulties to downstream ribbon handling equipment. Because of this non-uniformity, for example, special plates must be manufactured to have ribs of such a very-small thickness that the ribs can be received between the non-uniformly positioned hooks along the length of the ribbon of separable fastening element. Not only are such precisely-machined ribbed plates expensive, but any slight intolerance in either plate or rib position mashes the hooks, which results in a degradation, if not a total spoilation, of the product integrity.
A further disadvantage, insofar as production is concerned, is that the prior art is only capable of producing a single ribbon of separable fastening element. Although it is conceivable that the Menzin et al forming disk and associated machinery could be increased in diameter and scale to accommodate two injection heads and two removal stations, it would not in fact be feasible either economically or practicably. Because of the tight tolerances required of the several mold and spacer plates of each of the modules, a scaled machine, of the size necessary to accommodate, for example, dual injectors and removal stations, would cost between a multiple of four and nine of the cost of the original machine, which cost is prohibitive.